Flame retardant, phosphorus-containing polymers are well-known in the industry. These polymers can be used to impart a degree of flame resistance to cellulose-containing fabrics, such as cotton fabrics. The polymers typically are produced by padding a tetrahydroxymethyl phosphonium compound or a phosphonium precondensate (i.e., a precondensate made by reacting a tetrahydroxymethyl phosphonium compound with a limited amount of a cross-linking agent) onto a fabric and then reacting the phosphonium compound or precondensate with a suitable cross-linking agent. In certain embodiments of such known processes, the treated fabric is heated in order to accelerate the reaction between the phosphonium compound or precondensate and the cross-linking agent, which reaction yields the desired flame retardant, phosphorus-containing polymer. While heating accelerates the reaction, heating can also volatilize a significant portion of the phosphonium compound or precondensate deposited onto the fabric. This results in waste and increased cost since the volatilized phosphonium compound or precondensate imparts no benefit to the fabric. Also, the volatilized phosphonium compound or precondensate can form a build-up on the interior surfaces of the apparatus in which the fabric is heated, and this build-up must be periodically removed to ensure proper functioning of the apparatus. The downtime and expense of cleaning the apparatus also contributes to increased cost for the treated fabric.
Further, conventional processes typically require the addition of significant amounts of cross-linking agent in order to produce the desired phosphorus-containing polymer. This is true even when a commercially-available precondensate is used, since such precondensates are made with a limited amount of cross-linking agent (less than is needed to produce the desired polymer) and this limited amount of cross-linking agent has fully reacted with phosphonium compounds in the precondensate. This complete reaction means there are no more reactive groups (on moieties derived from the cross-linking agent) available to further react and propagate formation of the desired polymer. This necessitates the use of additional cross-linking agent when the polymer is produced. While this additional cross-linking agent is necessary, the presence of large amounts of “free” cross-linking agent can lead to side reactions that compete with reactions that form the desired polymer. These side reactions can produce polymers or segments within the phosphorus-containing polymer that deleteriously affect the performance and/or stability of the polymer.
A need therefore remains for improved precursors for flame retardant, phosphorus-containing polymers, and processes for producing such polymers that do not suffer from the disadvantages described above. A need also remains for processes for producing articles (e.g., fabrics) treated with such polymers. The invention described in this application aims to satisfy such needs.